1999 Mercruiser 5.7 with 2bbl MerCarb issues

My spring has gotten off to a bumpy start. Let me tell you the tale...

I have a 1999 Glastron GS225 with a Mercruiser 5.7L Thunderbolt V Alpha One Gen 2 stern drive. I started having issues that seemed carburetor related last year, so I replaced the carburetor. It had a 2bbl MerCarb on it (one idle mix adjustment screw) and I replaced it with a Rochester 2GC 2bbl. It ran OK, but rich (black smoke) and I could never get it quite right. So this spring I decided to rebuild the MerCarb (which I kept in my garage). It is a fairly simple carburetor, so I thought I could handle the job. I bought the rebuild kit, disassembled the MerCarb and soaked it in parts bath, then hosed it off with carburetor cleaner and let it dry. I reassembled it with the new power valve, needle/seat, accelerator pump, check ball, etc., set the float levels according to a Mercruiser Service Bulletin, which said to set the float level to 10 mm and the drop to 27 mm. I set the idle mix screw to 1 1/4 turns out, and adjusted the electric choke as specified in the bulletin.

The engine runs, but it ain't right. I can't get a smooth idle. It wants to die when the choke opens, even when the engine is nice and warm. It surges. It won't throttle up smoothly- it goes from a 6 or 7 hundred RPM idle to a roaring 2000 RPM instantly, no matter how gently the throttle is opened. I have to believe I missed something in the rebuild, but I can't figure out what. I replaced the spark plugs since the other carb was running rich, and while I had the plugs out I ran a compression test- all 8 cylinders were strong, between 160 and 180 psi on 4 strokes. Oil pressure is good- 40 psi even at a low stumbling idle. The spark plug wires, distributor cap and rotor were all replaced last fall. I'm grasping for ideas. Anybody have any thoughts? I appreciate any insight any of you can offer.

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

Ayuh,.... Welcome Aboard,....

Even in a fully equiped shop, a Carb Rebuild is a 50/ 50 shot, at Best....
'n compressed air is Mandatory...

You could try it again, or I'd probably throw on a new manifold, 'n a 4bbl. carb, myself...
The Edlebrock performer is reasonably cheap, 'n is Exactly the same as the Merc/ Weber carb that Merc is still using...

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

OK- so I go whole-hog and slap an Edelbrock Performer on there. What carburetor would you recommend, and what kind of linkage headaches can I expect? I'm assuming we're talking a new carb, since a rebuilt carb is a 50/50 shot...

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

OK- so I did a quick search, and I found the Edelbrock 1409 Performer 600 CFM marine carburetor with electric choke for $360. It is a square bore, and I don't see a lot of square bore manifolds. Any suggestions? Would you use a spread bore manifold and an adapter plate? What kind of linkage headaches are likely?

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

Hwhig said:

OK- so I did a quick search, and I found the Edelbrock 1409 Performer 600 CFM marine carburetor with electric choke for $360. It is a square bore, and I don't see a lot of square bore manifolds. Any suggestions? Would you use a spread bore manifold and an adapter plate? What kind of linkage headaches are likely?

Click to expand...

Ayuh,... Yer boat's a 99 you say, that should be Vortec heads,..??...
To tell, count the bolts holdin' the Intake, to the Heads....
Vortec uses 4 on each side, total 8....

You don't say if yer boatin' in freshwater, or brine,..??
If in brine, I hear Michigan Motors has the GM cast iron manifolds for it....
In freshwater,...
The aluminum Edlebrock works quite Nicely in that combination...
Buy a manifold to fit the heads, 'n the Carb....
Stay away from Adapters...

For the throttle linkage, 'n brackets,...
Hunt down the hardware used by Merc for their AFB/ Merc/ Weber carb they use in that same combo...
Ya oughta be able to find it used on ebay or somewhere....

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

I run the thing in freshwater only. Another interesting tidbit- Edelbrock square-bore carburetors (such as the 1409 marine carburetor which I am giving serious consideration to) will fit on a spread-bore Edelbrock manifold with no adapter plate! This tends to explain why there don't seem to be a lot of manifolds that are specifically square-bore. This conversion would end up cosing about $650, since I would also need a new flame arrestor. I would think this would be worth an extra 20 to 30 horses out of the motor- maybe more. I'm thinking about it...

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

I'm thinking about it...

Click to expand...

Ayuh,... I thought ya might,.. swhy I mentioned it....

Ya might wanta verify which hold down bolts the Mercruiser brackets fit, before ya decide which manifold pattern to get...

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

Have you ever checked the gas? Make sure theres no water in it.

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

ENSIGN said:

Have you ever checked the gas? Make sure theres no water in it.

Click to expand...

I LOOKED at the gas by pulling the fuel/water separating filter. I poured the contents of the filter into a glass jar to see if any water was immediately apparent. It wasn't. I'm not sure if that is good enough. I have a new float on the way for the MerCarb, just in case there is an issue with the old float. I did not weigh it. The new float was about $13, so I decided to just order the foolish thing and see if it helps. When the new float arrives, I will try the old "alternate fuel source" trick and feed nice fresh ethanol-free dinosaur juice to it and see if it behaves itself. If it does, I have no compunctions about ripping that big ol' 44-gallon plastic tank out of the belly of my boat and purging it- I have done it before. It isn't my favorite way to spend an afternoon, but you do what you gotta do...

I certainly hope that I can make this MerCarb behave itself. I don't NEED a 4 bbl. The boat performs quite well with the 2 bbl when everything is working right. All I am likely to get from a 4 bbl is worse fuel economy (and the thing is thirsty as it is).

Once I get the carb situation ironed out, I need to deal with the lower unit shift cable. The thing is VERY DIFFICULT to get into neutral. I understand that this is usually caused by a sticky/worn lower unit shift cable, which causes the shift "kill switch" to not work correctly. Anybody got sage advice on THAT project? (like- don't try it, pay a pro?)

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

I had the exact same issue with the 2 bl Rochester that I bought from I- 5, ran rich, black smoke. I ended up putting the Mercarb back on and it has been much better............ 5.0 Bravo 3

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

Installed the new float this evening. It runs a lot better. Now I need an opportunity to get it on the water...

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

One thing to remember when re-buildin a carb is to clean and re-clean a soak in carb soak,blow out with comp. air,scrub w/ soapy water, re-soak in carb dip blow out with air again and scrub with soapy water and blow it off yet again w/ air making sure every orafice is clear and clean I also coat all the gaskets in vasiline when assemblin so they don't stick to mating parts if need to dis-assemble.

Re: 1999 Mercruiser 5.7 with 2bbl MerCarb issues

HOT DOG!!! I got the thing out on the water last night and she purrs like a kitten and runs like a scalded dog! Runs better than it ever has during my ownership of it. If you rebuild a MerCarb, get a new float. They aren't expensive and it is one less thing to worry about.